Prolactin (PRL)-secreting tumors are the most common form of functioning pituitary tumor. Most are microadenomas (<1 cm in size) and usually present with galactorrhea, disturbance of menstrual regularity, infertility, and, in the male, decreased sexual function (1,2). Diagnosis is made by measurement of circulating PRL and pituitary imaging. Spurious hyperprolactinemia may result from measurement of complexed but bioinactive macroprolactin, and an extraction assay should be considered in all patients who have elevated serum PRL on conventional testing, especially where the level is discordant with the clinical presentation. In general, preservation of normal anterior and posterior pituitary function is the rule in patients with PRL-secreting microadenomas, but assessment of basal hormone levels is recommended in all patients.
The initial treatment of prolactinomas involves the use of oral dopamine agonist therapy. Rapid reduction in PRL levels and shrinkage of both micro adenomas and macroadenomas occur in the majority of patients (3). In general, pituitary function is unaffected, but infarction has been described, which may result in loss of adenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), growth hormone (GH) and gonadotropins. Monitoring of basal levels and performance of dynamic testing, as outlined in Appendix 1 (see p. 197 et seq.), is recommended, particularly in macroadenomas.
In rare cases, dopamine agonist therapy is unsuccessful, often related to non-compliance, poor tolerance, or adverse effects. However, before diagnosing intolerance or resistance, a second agent, such as cabergoline or quinagolide, should be tried. When true resistance is diagnosed, pituitary surgery and/or external beam irradiation may be considered. Larger more invasive tumors are less likely to be cured by surgery, as are those patients with the highest preoperative prolactin levels (4). After a surgical procedure, assessment of ACTH reserve, water balance, TSH, GH, and gonadotrophin reserve should be performed before discharge, as outlined in the next subheading. Long-term surveillance of anterior pituitary function is necessary after irradiation to assess the reserve of GH and other pituitary hormones. Surveillance of the pituitary fossa and endocrine assessment should follow the model outlined for the treatment of acromegaly (next subheading).
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